#include <stdio.h>


int main() {
    int n, flag = 1;
    double temp;
    double sum = 0;
    scanf("%d", &n);    
    for (int i = 1; i <= n; i++) {
        temp = flag * i * 1.0 / (2 * i - 1);
        sum += temp;
        flag = -flag;
    }
    printf("%.6lf", sum);
    return 0;
}
